This work describes a data cleaning procedure for the detection of eddy covariance fluxes affected by systematic errors. We believe that the proposed procedure can serve as a basis toward a unified quality control strategy suitable for the centralized data processing pipelines, where the use of completely data-driven and scalable procedures that guarantee high-quality standards and reproducibility of the released products constitutes an essential prerequisite.

We test the approach of producing global gridded carbon fluxes based on combining machine learning with local measurements, remote sensing and climate data. We show that we can reproduce seasonal variations in carbon assimilated by plants via photosynthesis and in ecosystem net carbon balance. The ecosystem’s mean carbon balance and carbon flux trends require cautious interpretation. The analysis paves the way for future improvements of the data-driven assessment of carbon fluxes.

Soil heterotrophic respiration (HR) is an important component of land–atmosphere carbon exchange but is difficult to observe globally. We analyzed the imprint that this flux leaves on atmospheric CO2 using a set of simulations from HR models with common inputs. Models that represent microbial processes are more variable and have stronger temperature sensitivity than those that do not. Our results show that we can use atmospheric CO2 observations to evaluate and improve models of HR.

Causal inference promises new insight into biosphere–atmosphere interactions using time series only. To understand the behaviour of a specific method on such data, we used artificial and observation-based data. The observed structures are very interpretable and reveal certain ecosystem-specific behaviour, as only a few relevant links remain, in contrast to pure correlation techniques. Thus, causal inference allows to us gain well-constrained insights into processes and interactions.

We present the highest resolution solar-induced chlorophyll fluorescence (SIF) dataset from satellite measurements, providing previously unobservable phenomena related to plant photosynthesis. We find a strong correspondence between TROPOMI SIF and AmeriFlux GPP. We then observe a double peak in the seasonality of California's photosynthesis, not seen by traditional vegetation indices (e.g., MODIS). This is further corroborated by EOF/PC analysis.

Commonly used nitrogen fertilisers, ammonium nitrate, urea and urea coated with a urease inhibitor, were applied to experimental plots. Fertilisation with ammonium nitrate supported the largest yields but also resulted in the largest nitrous oxide emissions. Urea was the largest emitter of ammonia. The coated urea did not significantly increase yields; however, ammonia emissions were substantially smaller than urea. The coated urea was the best environmentally but is economically unattractive.

The effect of soil water availability (SWA) on emissions of isoprenoids by trees was studied by setting up a parameterization from published data. SWA impact on isoprene emissions can be described by a growth type curve, while monoterpene emissions display a pattern reflecting plants’ stomata opening. Sesquiterpene fluxes tend to increase at the start of severe drought until resources decline. Feedbacks on atmospheric processes such as ozone and aerosol particles are further studied.

The tundra plays a pivotal role in Arctic mercury cycling by storing atmospheric mercury deposition and shuttling it to the Arctic Ocean. We used the isotopic fingerprint of mercury to investigate the processes controlling atmospheric mercury deposition. We found that the uptake of atmospheric mercury by vegetation was the major deposition source. Direct deposition to snow or soils only played a minor role. These results improve our understanding of Arctic mercury cycling.

Key findings are the nearly optimal response of T to atmospheric water vapor pressure deficits across methods and scales. Additionally, the notion that T / ET intermittently approaches 1, which is a basis for many partitioning methods, does not hold for certain methods and ecosystems. To better constrain estimates of E and T from combined ET measurements, we propose a combination of independent measurement techniques to better constrain E and T at the ecosystem scale.

We show the response of a commercial oil palm plantation in Indonesia to the extreme El Niño–Southern Oscillation (ENSO) event in 2015. Our measurements and model suggest that without human-induced forest fires and related smoke emissions, the observed negative impact on oil palm carbon dioxide greenhouse gas fluxes, carbon accumulation and yield due to ENSO-related drought would have been less pronounced. With respect to climate change we highlight the importance of fire prevention in the area.

This study examines how limited water availability during droughts affects water-use efficiency. This metric describes how much carbon an ecosystem can assimilate for each unit of water lost by transpiration. We test how well different water-use efficiency models can capture the dynamics of transpiration decrease due to increased soil-water limitation. Accounting for the interacting effects of radiation and water limitation is necessary to accurately predict transpiration during these periods.

Human activities strongly interfere in the land–atmosphere interactions through changes in land use and land cover changes and land management. The objectives of this review are to synthesize the existing experimental and modelling works that investigate physical, chemical, and biogeochemical interactions between land surface and the atmosphere. Greater consideration of atmospheric chemistry, through land–atmosphere interactions, as a decision parameter for land management is essential.

Fatty alcohols (FAs) are major components of surface lipids and can act as surface-active atmospheric organic aerosols, influencing the cloud formation. We identified five secondary FAs in atmospheric aerosols at two temperate forest sites and revealed their distinct seasonal variation for the first time. Our results suggest that they originated mostly from plant wax and could be used as useful tracers for primary biological aerosol particles.

In the Sahel region during the wet season, CO2 and NO are released to the atmosphere, and NH3 is deposited on the soil. During the dry season, processes are strongly reduced. This paper shows the temporal variation in these soil–atmosphere exchanges of trace gases for 2 years, their sharp increase when the first rains fall onto dry soils, and how microbial processes are involved. We use a modelling approach, which is necessary when continuous measurements are not possible in remote regions.

Although coastal regions only amount to 7 % of the global oceans, their contribution to the global oceanic surface exchange of CO2 is much greater. In this study, we gain detailed insight into how these coastal marine fluxes compare to CO2 exchange from coastal land regions. Annually, the coastal marine exchanges are smaller than the total uptake of CO2 from the land surfaces within the study area but comparable in size to terrestrial fluxes from individual land cover classes of the region.

We compared the energy balance closure (EBC) under varying environmental conditions and investigated a wide range of possible reasons for the energy imbalance. As measures for the imbalance, we used ordinary linear regression, the energy balance ratio (EBR), and the energy residual. The EBR was also investigated as a function of buoyancy, friction velocity, and atmospheric stability. Moreover, the relationship between the EBC and flux source area or footprint was also investigated.

We analysed ecosystem-scale measurements of methane exchange between Arctic tundra and the atmosphere, taking into account the large variations in vegetation and soil properties. The measurements are spatial averages, but using meteorological and statistical modelling techniques we could estimate methane emissions for different land cover types and quantify how well the measurements correspond to the spatial variability. This provides a more accurate estimate of the regional methane emission.

We have compared global carbon budgets calculated from numerical inverse models and CO2 observations, and evaluated how these systems reproduce vertical gradients in atmospheric CO2 from aircraft measurements. We found that available models have converged on near-neutral tropical total fluxes for several decades, implying consistent sinks in intact tropical forests, and that assumed fossil fuel emissions and predicted atmospheric growth rates are now the dominant axes of disagreement.

Accounting for the vegetation signal is critical for comprehensive CO2 budget assessment in China. We model and evaluate hourly vegetation carbon dioxide (CO2) exchange (mass per unit area per unit time) in northern China from 2005 to 2009. The model is driven by satellite and meteorological data, is linked to ground-level ecosystem observations, and is applicable to other time periods. We find vegetation uptake of CO2 in summer is comparable to emissions from fossil fuels in northern China.

We explored the timing of the peak of the short annual growing season in tundra ecosystems as indicated by an extensive suite of satellite indicators of vegetation productivity. Delayed peak greenness compared to peak photosynthesis is consistently found across years and land-cover classes. Plants also experience growth after optimal conditions for assimilation regarding light and temperature have passed. Our results have implications for the modelling of the circumpolar carbon balance.

Carbon fixed by plants and phytoplankton through photosynthesis is ultimately stored in soils and sediments or released to the atmosphere during decomposition of dead biomass. Carbon-use efficiency is a useful metric to quantify the fate of carbon – higher efficiency means higher storage and lower release to the atmosphere. Here we summarize many definitions of carbon-use efficiency and study how this metric changes from organisms to ecosystems and from terrestrial to aquatic environments.

Using a simulation study and field data, we quantify the biases that can be introduced in fluxes measured by eddy covariance (EC) if the raw high-frequency data are affected by random and systematic timing misalignments. Our study was motivated by the increasingly widespread adoption of fully digital EC systems potentially subject to such timing errors. We found biases as large as 10 %. We further propose a test to evaluate EC data logging systems for their time synchronization capabilities.

We have developed an accurate method (SynFlux) to estimate ozone deposition and stomatal uptake across 103 flux tower sites (43 US, 60 Europe), where ozone concentrations and fluxes have not been measured. In all, the SynFlux public dataset provides monthly values of ozone dry deposition for 926 site years across a wide array of ecosystems. The SynFlux dataset will promote further applications to ecosystem, air quality, or climate modeling across the geoscience community.

It is of great interest to know whether croplands act as a net source or sink of atmospheric CO2 and if soil carbon (C) stocks are preserved over long timescales due to the role of C in soil fertility. For a cropland in Switzerland it was found that managing the field under the Swiss framework of the Proof of Ecological Performance (PEP) resulted in soil C losses of 18.0 %. Additional efforts are needed to bring Swiss management practices closer to the goal of preserving soil C in the long term.

Net fluxes of carbon dioxide at the ecosystem level measured by eddy covariance are a main source for understanding biosphere–atmosphere interactions. However, there is a need for more usable and extensible tools for post-processing steps of the half-hourly flux data. Therefore, we developed the REddyProc package, providing data filtering, gap filling, and flux partitioning. The extensible functions are compatible with state-of-the-art tools but allow easier integration in extended analysis.

We investigated the roles that weather and forest disturbances like drought play in shaping changes in ecosystem photosynthesis and carbon exchange in an Amazon forest. We discovered that weather largely influenced differences between years, but a prior drought, which occurred 3 years before measurements started, likely hampered photosynthesis in the first year. This is the first atmospheric evidence that drought can have legacy impacts on Amazon forest photosynthesis.

From seasonal in situ observations on how a Mediterranean ecosystem responds to drought, a specific isoprene emission (ER, emission rates) algorithm was developed, upon which 2100 projections (IPCC RCP2.6 and RCP8.5 scenarios) were made. Emission rates were found to be mainly sensitive to future temperature changes and poorly represented by current empirical emission models. Drought was found to aggravate thermal stress on emission rates.

Earth system models (ESMs) project future changes in climate in response to changes in anthropogenic emissions of greenhouse gases (GHGs). However, before this can be achieved the natural fluxes of a given GHG must also be modelled. This paper evaluates the natural methane fluxes simulated by the CLASS-CTEM model (which is the land component of the Canadian ESM) against observations to show that the simulated methane emissions from wetlands and fires, and soil uptake of methane are realistic.

To understand future food security, it is critical to develop realistic crop models with reliable sensitivity to environmental factors. We find that particulate matter (PM) causes a significant, but smaller, enhancement for global wheat and rice production than estimated without nutrient and physiological limitations imposed by a crop model. In contrast, maize grows near its physiological maximum, with little enhancement from PM. Nitrogen deposition leads to a small increase in crop production.

Oxidative weathering of sedimentary rocks can release carbon dioxide to the atmosphere. Here, we designed a chamber-based method to measure these CO2 emissions directly for the first time. The chamber is drilled in the rock and allows us to collect the CO2 to fingerprint its source using carbon isotopes. We tested our method in Draix (France). The measured CO2 fluxes were substantial, with ~20% originating from oxidation of the rock organic matter and ~80% from dissolution of carbonate minerals.

This study shows that leaf quantity and leaf age have an important effect on seasonal changes in isoprene emissions and that these could play an even more important role in regulating ecosystem isoprene fluxes than light and temperature at seasonal timescales in tropical forests. These results bring novelty and new insight for future research because in the past leaf phenology was not considered as an important factor that controls biological processes in the tropics.

Biogenic isoprene fluxes are simulated over Europe with the MEGAN–MOHYCAN model for the recent past and end-of-century climate at high spatiotemporal resolution (0.1°, 3 min). Due to climate change, fluxes increased by 40 % over 1979–2014. Climate scenarios for 2070–2099 suggest an increase by 83 % due to climate, and an even stronger increase when the potential impact of CO2 fertilization is considered (up to 141 %). Accounting for CO2 inhibition cancels out a large part of these increases.

We report the seasonality of net ecosystem–atmosphere CO2 exchange (NEE) in a temperate evergreen broadleaved forest in Sydney, Australia. We investigated how carbon exchange varied with climatic drivers and canopy dynamics (leaf area index, litter fall). We found that our site acted as a net source of carbon in summer and a net sink in winter. Ecosystem respiration (ER) drove NEE seasonality, as the seasonal amplitude of ER was greater than gross primary productivity.

Measurements of the trace gas carbonyl sulfide (OCS) are helpful in quantifying photosynthesis at previously unknowable temporal and spatial scales. While CO2 is both consumed and produced within ecosystems, OCS is mostly produced in the oceans or from specific industries, and destroyed in plant leaves in proportion to CO2. This review summarizes the advancements we have made in the understanding of OCS exchange and applications to vital ecosystem water and carbon cycle questions.

Tropospheric ammonia is mainly emitted by agriculture. It constitutes a loss for the farmers and a threat to human health and the environment. It is therefore crucial to improve agricultural practices to reduce ammonia losses following fertilisation. In this study we propose an inverse dispersion modelling method to simultaneously quantify ammonia volatilisation from multiple small agronomic plots. The method was evaluated to be suitable (though slightly biased) based on a theoretical study.

(1) We obtained a better understanding of wet dissolved carbon deposition during a concentrated rainy season at a semi-arid catchment in the Loess Plateau region. (2) Wet dissolved carbon deposition concentration exhibited large variations and may be influenced by dissolved carbon source, rainfall characteristics, and the interactions between ions. (3) The estimated annual DOC and DIC deposition fluxes were 1.91 and 1.89 g C m−2 yr−1 and indicated a substantial input to the semi-arid catchment.

The ecosystem is a significant sink of carbon dioxide. To quantify this sink, very complex and validated models are required. However, the comparison of modeled and measured energy and matter fluxes in a heterogeneous landscape is still a challenge. On the one hand, models must be applied for various surface types, while on the other hand the comparison of the fluxes is only possible based on the flux source areas. This paper treats the potential aggregation of modeled fluxes and its validation.

Our work systematically quantifies extreme heat and drought event impacts on gross primary productivity (GPP) and ecosystem respiration globally across a wide range of ecosystems. We show that heat extremes typically increased mainly respiration whereas drought decreased both fluxes. Combined heat and drought extremes had opposing effects offsetting each other for respiration, but there were also strong reductions in GPP and hence the strongest reductions in the ecosystems carbon sink capacity.

We proposed a new data processing technique to reduce the uncertainty of H2O fluxes measured using the eddy covariance method, which is widely used to observe mass/energy fluxes between biosphere and atmosphere. A special feature of the proposed technique is the merging of two existing methods a new method. Such a strategy strengthens the strength and makes up for the weakness of the original methods. It will contribute to the standardization of eddy covariance data processing.

Isoprene flux measurements made above five European oak forests were reviewed to generate new emission potentials. Six variations of the Guenther algorithms were inverted to back out time series of isoprene emission potential, and then an “average” emission potential was determined using one of four commonly used approaches. Our results show that emission potentials can vary by up to a factor of 4 and highlight the need for the community to now harmonize their approach to reduce uncertainty.

From the analysis of MODIS and Landsat satellite data of the Jambi province in Indonesia, this first study on the effects of oil palm expansion on the surface temperature in Indonesia shows shows a local and regional warming effect caused by the expansion of oil palm plantations and other cash or tree crops between 2000 and 2015. The observed warming effects may affect ecosystem services, reduce water availabilty in the dry period and increase the vulnerability to fires in the province.

According to this study, Artemisia ordosica escaped water limitations by invoking a water-conservation strategy with the regulation of stomatal conductance and advancement of sap-flow peaking time, manifesting in a hysteresis effect. This study provides a significant contribution to the understanding of acclimation processes in desert-shrub species to drought-associated stress in dryland ecosystems.

An improvement in our process-based understanding of CO2 exchanges in the Arctic and their climate sensitivity is critical. With continued warming temperatures and longer growing seasons, tundra systems will likely increase rates of C cycling, although shifts in sink strength could take place, challenging the forecast of upcoming C states. In this context, we investigated the functional responses of C exchange to environmental characteristics across 8 consecutive years in West Greenland.

We investigated the response of water use efficiency (WUE) to summer drought in a boreal Scots pine forest (Pinus sylvestris) on the daily time scale mainly using EC flux data from the Hyytiälä (southern Finland) flux site. Simulation results from the JSBACH land surface model were also evaluated against the observed results. The performance of three WUE metrics at the ecosystem level (EWUE, IWUE, and uWUE) during the severe summer drought were studied and showed different results.

This study describes and evaluates a new ammonia (NH3) exchange model for grazed fields (GAG_field). GAG_field is able to simulate the main features of the observed NH3 fluxes. A sensitivity analysis for the non-meteorological model parameters showed that the sensitivity of the NH3 fluxes to a parameter varies among urine patches. Moreover, the fluxes modelled with a dynamic soil pH are similar if a constant pH 7.5 is used, suggesting a useful simplification for regional-scale model application.

Water, Energy, and Carbon with Artificial Neural Networks (WECANN) is a statistically based estimate of global surface latent and sensible heat fluxes and gross primary productivity. The retrieval uses six remotely sensed observations as input, including the solar-induced fluorescence. WECANN provides estimates on a 1° × 1° geographic grid and on a monthly time scale and outperforms other global products in capturing the seasonality of the fluxes when compared to eddy covariance tower data.

Here we synthesize a wide range of global spatiotemporal observational data on carbon exchanges between the Earth surface and the atmosphere. A key challenge was to consistently combining observational products of terrestrial and aquatic surfaces. Our primary goal is to identify today’s key uncertainties and observational shortcomings that would need to be addressed in future measurement campaigns or expansions of in situ observatories.